This invention relates to a synthetic resin shell shoe that can be easily and inexpensively mass produced. More specifically, the shell has ventilation for inhibiting dampness and heating as well as protection to prevent the intrusion of water into the shoe.
Because of the beauty and ventilation provided by natural leather, it is often used for the shell of high quality shoes. However, as well as providing ventilation, water can permeate through natural leather by capillary attraction. Therefore, natural leather has the disadvantage that the shoe becomes wet in rainy weather. Further, because leather, originally in sheet form, must be formed, with the midsole attached beneath, into a three dimensional surface in the shape of the foot, it also has the drawbacks that manufacture requires extensive labor, advanced techniques, and is a costly process. Still further drawbacks are loss of shape resulting from forming an inherently two dimensional sheet material into a three dimensional shape, and difficulty in producing shoes with wearing comfort similar to that of athletic shoes because of leather's inability to stretch sufficiently.
The inventor has developed a shoe with a shell partially formed from synthetic resin to solve the problems associated with natural leather (Japanese Public Disclosure No. 38241/1982).
The shoe of the present invention has the following features. Because the shell is molded as a three dimensional surface following the contour of the foot, it can be mass produced inexpensively compared with a natural leather shell. Because the shell form fits the surface of the foot and is stretchable, local regions of the shell do not get over stressed and the shoe can easily be worn for long periods with comfort. Further, because the three dimensional shape is formed with a mold, the shoe does not lose its shape.
Moreover, by galvanically etching the inner surface of the shell mold, a three dimensional pattern resembling that of natural leather can be imprinted on the surface of the synthetic resin shell. Consequently, a synthetic resin shell shoe with a handsomely patterned outer surface indistinguishable from that of high quality natural leather can be produced.
However, the principal and only drawback of a synthetic resin shell shoe is the lack of the important factor, ventilation. Consequently, if a synthetic resin shoe with the ventilating properties of natural leather or cloth were possible, an essentially ideal shoe could be produced.
Ventilation can be provided to a synthetic resin shell by forming a mesh pattern or large holes through the shell. However, like the former leather shoe, a shell with this configuration allows water to enter the shoe as well as air, and has the drawback that the foot gets wet when the shoe is worn in rainy weather. An all weather shoe cannot be realized in this fashion.
Over a period of many years of various experimentation and trial and error utilizing novel material properties, the inventor has tried to develop a synthetic resin shell having the apparent contradicting properties of ventilation and water protection. A synthetic resin shell has an extremely different structure from the dense collection of numerous fibers constituting natural leather, and consequently the inside of the synthetic resin shell does not absorb water by capillary action. Specifically, the synthetic resin shell is formed by injecting molten synthetic resin into a mold of the designated shape, and the shell formed by this process is essentially filled without gaps or holes with synthetic resin. It is well known that a shell with this structure does not allow either water or air to pass through it, does not absorb water, and has the unique property of repelling water.
By effective application of a unique physical property, namely surface tension, which is also responsible for the capillary action that causes water absorption by natural leather, the inventor has succeeded in developing a synthetic resin shell providing sufficient ventilation while effectively preventing water from permeating the ventilation holes into the shoe.